At the time when a gas water heater operates, a substantial amount of flue gas is discharged, and the temperature reaches up to 180° C. or so. A common gas water heater fails to utilize such a portion of heat and the heat is wasted. In addition, when the high-temperature flue gas, which may reach up to 180° C. or so is discharged by the gas water heater, a heat transfer heats up a body and a user may be burnt.
In order to efficiently utilize the high-temperature flue gas mentioned above and prevent the body from overheating, a condensing gas water heater is available. The condensing gas water heater further comprises condensing heat exchangers when compared with a common gas water heater, and the heat in the high-temperature flue gas is absorbed by the condensing heat exchanger, so as to heat cold water, and hence to achieve the effects of energy saving and environmental protection. As a result, the temperature of the flue-gas ultimately discharged can be significantly decreased and users are prevented from getting burnt. In a word, a condensing gas water heater has become increasingly valued and popular with the public, owing to characteristics of energy saving and environmental protection.